Optical disk, and method and apparatus for reproducing information recorded in optical disk

ABSTRACT

An optical disk is provided for recording data of a signal modulated according to a predetermined modulation method in a form of concavo-convex pits. The optical disk includes a first area having a reflecting film partly removed, and a second area for recording pits which are different from pits satisfying requirements of the predetermined modulation method. The first area having the reflecting film partly removed includes a portion which is formed by removing the reflecting film, and has a length longer than a maximum pit length determined by the modulation method in a circumferential direction of the optical disk. When the pits recorded on the optical disk are physically copied as they are, physical copying of the optical disk can be prevented by utilizing such a difference that the authorized optical disk differs from a pirated copy in a combination of the respective reproduced signals of the first and second areas.

This application is a divisional application of Ser. No. 09/677,595,filed Oct. 3, 2000, now U.S. Pat. No. 6,661,768.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical disk for recordingcopyrighted content information, and a method and an apparatus forreproducing copyrighted content information recorded in an optical disk.

2. Description of the Related Art

In recent multimedia societies, optical disks such as a CD-ROM and a DVDhave become remarkably widespread. With the widespread use of theoptical disks, so-called pirated ROM disks have appeared and allow apirate to benefit from the disk without compensating a copyright ownerby fraud by illegally making a pirated copy of the optical disk. Thepercentage of pirated copies of disks is rapidly increasing. Illegalcopying of the optical disk can take place in the following manner.Generally speaking, a pirate purchases an authorized optical disk, makesa master tape by reproducing information recorded on the optical disk bymeans of a disk drive, and mass-produces the pirated copies from themaster tape by the same method as a general disk manufacturing method.

In order to protect against the above-mentioned unauthorized copying,some optical disks are devised so that they can be reproduced by only aplayer designed specifically for them. As this type of optical disk, forexample, there is disclosed in the Japanese Patent Laid-Open PublicationNo 7-85574 a method including the steps of recording main information onan optical recording medium using a predetermined coding means, storingkey information indicating decoding means for decoding the maininformation in a form of a barcode symbol in a mirror surface area orthe like, reading our the key information by a reproducing apparatus,decoding and reproducing the main information utilizing a coding methodindicated by the key information.

The above-mentioned method of protecting against unauthorized copyinghas such a very excellent advantage that a general optical disk playercannot reproduce the optical disk. However, the method is helplessagainst and cannot protect against copying means for performing copyinginvolving no reproducing operation, i.e., for physically copying ortransferring concavo-convex pits of data of a signal recorded on anoptical disk surface as they are. This copying method requires noreproducing means, and can copy concavo-convex pit information of theoptical disk as it is even though original data of signal to be recordedon the optical disk is made sophisticated and complicated. Therefore,the above mentioned method of protecting against unauthorized copying isuseless.

SUMMARY OF THE INVENTION

An essential object of the present invention is, therefore, to providean optical capable of protecting against copying means for physicallycopying concavo-convex pits of data of a signal recorded on an opticaldisk surface as they are.

Another object of the present invention is to further provide a methodand apparatus for reproducing information recorded on the optical diskcapable of protecting against copying means for physically copyingconcavo-convex pits of data of a signal recorded on an optical disksurface as they are.

In order to achieve the aforementioned objective, according to oneaspect of the present invention, there is provided an optical disk forrecording data of a signal modulated according to a predeterminedmodulation method in a form of concavo-convex pits, the optical diskcomprising:

a first area having a reflecting film partly removed; and

a second area for recording pits which are different from pitssatisfying requirements of the predetermined modulation method.

According to another aspect of the present invention, there is providedan optical disk for recording data of a signal modulated according to apredetermined modulation method in a form of concavo-convex pits, theoptical disk comprising:

a first area having a reflecting film partly removed;

a second area for recording pits which are different from pitssatisfying requirements of the predetermined modulation method;

a first area location information recording area for recording locationinformation of the first area on the disk; and

a second area location information recording area for recording locationinformation of the second area on the disk.

In the above-mentioned optical disk, the first area having thereflecting film partly removed is preferably included in a user datarecording area for recording user data therein.

In the above-mentioned optical disk, the first area having thereflecting film partly removed preferably includes a portion, which isformed by removing the reflecting film, and which has a length longerthan a maximum pit length determined by the requirements of themodulation method, in a circumferential direction of the optical disk.

In the above-mentioned optical disk, each of the pits recorded in thesecond area is preferably longer than a maximum pit length determined bythe modulation method.

In the above-mentioned optical disk, each of the pits recorded in thesecond area is preferably longer than a maximum pit length determined bythe modulation method, and

wherein edges in the center of each of the pits recorded in the secondarea are inclined more gradually than edges in an end portion of each ofthe pits.

In the above-mentioned optical disk, the first area location informationrecording area and the second area location information recording areaare preferably recorded in an area except for a user data recording areafor recording user data therein.

According to a further aspect of the present invention, there isprovided a method for reproducing information recorded on an opticaldisk which is provided for recording data of a signal modulatedaccording to a predetermined modulation method in a form ofconcavo-convex pits, the optical disk comprising a first area having areflecting film partly removed, and a second area for recording pitswhich are different from pits satisfying requirements of thepredetermined modulation method, the method including the steps of:

detecting an area having the reflecting film partly removed, inaccordance with a reproduced signal of the first area;

detecting a pit which is different from the pit satisfying therequirements of the predetermined modulation method, in accordance witha reproduced signal of the second area; and

judging whether or not the information recorded on the optical diskshould be reproduced, in accordance with results detected by the twosteps of detecting.

According to a still further aspect of the present invention, there isprovided a method for reproducing information recorded on an opticaldisk which is provided for recording data of a signal modulatedaccording to a predetermined modulation method in a form ofconcavo-convex pits, the optical disk comprising a first area having areflecting film partly removed, a second area for recording pits whichare different from pits satisfying requirements of the predeterminedmodulation method, a first area location information recording area forrecording location information of the first area on the disk, and asecond area location information recording area for recording locationinformation of the second area on the disk, the method including thesteps of:

reproducing information recorded in the first area in accordance withthe location information of the first area on the disk recorded in thefirst area location information recording area, and outputting areproduced signal of the first area;

reproducing information recorded in the second area in accordance withthe location information of the second area on the disk recorded in thesecond area location information recording area, and outputting areproduced signal of the second area;

detecting an area having the reflecting film partly removed, inaccordance with the reproduced signal of the first area;

detecting a pit which is different from the pit satisfying therequirements of the predetermined modulation method, in accordance withthe reproduced signal of the second area; and

judging whether or not the information recorded on the optical diskshould be reproduced, in accordance with results detected by the twosteps of detecting.

In the above-mentioned method, the step of reproducing informationrecorded in the first area preferably includes the step of reproducinginformation recorded in the first area in a defocus state.

In the above-mentioned method, the step of reproducing informationrecorded in the first area preferably includes the step of reproducingthe information recorded in the first area by performing tracking anarea located between two adjacent tracks.

In the above-mentioned method, the step of detecting the area having thereflecting film partly removed preferably includes the step of detectingwhether or not the reflecting film is removed on the two adjacenttracks.

According to a still further aspect of the present invention, there isprovided an apparatus for reproducing information recorded on an opticaldisk which is provided for recording data of a signal modulatedaccording to a predetermined modulation method in a form ofconcavo-convex pits, the optical disk comprising a first area having areflecting film partly removed, and a second area for recording pitswhich are different from pits satisfying requirements of thepredetermined modulation method, the apparatus comprising:

a first area detecting circuit for detecting the first area inaccordance with a reproduced signal from the optical disk uponreproducing information recorded in the first area, and outputting afirst detecting signal;

a second area detecting circuit for detecting the second area inaccordance with a reproduced signal from the optical disk uponreproducing information recorded in the second area, and outputting asecond detecting signal; and

judging means for judging whether or not the information recorded on theoptical disk should be reproduced, in accordance with the first andsecond detecting signals.

According to a still further aspect of the present invention, there isprovided an apparatus for reproducing information recorded on an opticaldisk which is provided for recording data of a signal modulatedaccording to a predetermined modulation method in a form ofconcavo-convex pits, the optical disk comprising a first area having areflecting film partly removed, a second area for recording pits whichare different from pits satisfying requirements of the predeterminedmodulation method, a first area location information recording area forrecording location information of the first area on the disk, and asecond area location information recording area for recording locationinformation of the second area on the disk, the apparatus comprising:

a first detecting window generating circuit for generating a firstdetecting window signal in accordance with the location information ofthe first area on the disk recorded in the first area locationinformation recording area;

a second detecting window generating circuit for generating a seconddetecting window signal in accordance with the location information ofthe second area on the disk recorded in the second area locationinformation recording area;

a first area detecting circuit for detecting the first area inaccordance with a reproduced signal from the optical disk uponreproducing information recorded in the first area, and outputting afirst detecting signal;

a second area detecting circuit for detecting the second area inaccordance with a reproduced signal from the optical disk uponreproducing information recorded in the second area, and outputting asecond detecting signal; and

judging means for judging whether or not the information recorded on theoptical disk should be reproduced, in accordance with the firstdetecting signal in a valid time interval of the first detecting windowsignal, and the second detecting signal in a valid time interval of thesecond detecting window signal.

In the above-mentioned apparatus, the first area detecting circuitpreferably comprises a first comparator for comparing the reproducedsignal from the optical disk upon reproducing information recorded inthe first area, with a predetermined first threshold value, andoutputting a first comparison result signal.

In the above-mentioned apparatus, the second area detecting circuitpreferably comprises:

a second comparator for comparing the reproduced signal from the opticaldisk upon reproducing information recorded in the second area, with apredetermined second threshold value, and outputting a second comparisonresult signal;

a third comparator for comparing the reproduced signal from the opticaldisk upon reproducing information recorded in the second area, with apredetermined third threshold value, and outputting a third comparisonresult signal; and

an arithmetic logic circuit for performing a logic operation between thesecond comparison result signal and the third comparison result signal,and outputting a logic operation result signal.

In the above-mentioned apparatus, the first area detecting circuitpreferably detects the first area in accordance with a reproduced signalfrom the optical disk upon reproducing information recorded on a trackincluding the first area, and a reproduced signal from the optical diskupon reproducing information recorded on a further track including thefirst area and adjacent to the track, and outputs the first detectingsignal.

According to a further aspect of the present invention, there isprovided a method for reproducing information recorded on an opticaldisk which is provided for recording data of a signal modulatedaccording to a predetermined modulation method in a form ofconcavo-convex pits, the optical disk comprising a first area having areflecting film partly removed, the method including the steps of:

detecting the first area in accordance with a reproduced signal from theoptical disk upon reproducing information recorded in the first area,and outputting a first detecting signal; and

judging whether or not the information recorded on the optical diskshould be reproduced, in accordance with the first detecting signal.

In the above-mentioned method, the step of detecting the first area andoutputting the first detecting signal preferably includes the step of:

detecting the first area in accordance with a reproduced signal from theoptical disk upon reproducing information recorded on a track includingthe first area, and a reproduced signal from the optical disk uponreproducing information recorded on a further track including the firstarea and adjacent to the track, and outputting the first detectingsignal.

In the above-mentioned method, the step of detecting the first area andoutputting the first detecting signal preferably includes the step of:

judging whether or not the first area is detected in accordance withwhether or not a first number of data from a predetermined sectoraddress to the detected first area, which is counted based on thereproduced signal from the optical disk upon reproducing informationrecorded on the track including the first area, substantially coincideswith a second number of data from the sector address to the detectedfirst area, which is counted based on the reproduced signal from theoptical disk upon reproducing information recorded on a further trackincluding the first area and adjacent to the track.

According to a still further aspect of the present invention, there isprovided an apparatus for reproducing information recorded on an opticaldisk which is provided for recording data of a signal modulatedaccording to a predetermined modulation method in a form ofconcavo-convex pits, the optical disk comprising a first area having areflecting film partly removed, the apparatus comprising:

detecting means for detecting the first area in accordance with areproduced signal from the optical disk upon reproducing informationrecorded in the first area, and outputting a first detecting signal; and

judging means for judging whether or not the information recorded on theoptical disk should be reproduced, in accordance with the firstdetecting signal.

In the above-mentioned apparatus, the detecting means preferably detectsthe first area in accordance with a reproduced signal from the opticaldisk upon reproducing information recorded on a track including thefirst area, and a reproduced signal from the optical disk uponreproducing information recorded on a further track including the firstarea and adjacent to the track, and outputs the first detecting signal.

In the above-mentioned apparatus, the detecting means preferably judgeswhether or not the first area is detected in accordance with whether ornot a first number of data from a predetermined sector address to thedetected first area, which is counted based on the reproduced signalfrom the optical disk upon reproducing information recorded on the trackincluding the first area, substantially coincides with a second numberof data from the sector address and the detected first area, which iscounted based on the reproduced signal from the optical disk uponreproducing information recorded on a further track including the firstarea and adjacent to the track.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome clear from the following description taken in conjunction withthe preferred embodiments thereof with reference to the accompanyingdrawings throughout which like parts are designated by like referencenumerals, and in which:

FIG. 1 is a plan view showing a planar structure of an optical disk 1according to a first preferred embodiment of the invention;

FIG. 2 is a sectional view showing a sectional structure of the opticaldisk 1 shown in FIG. 1;

FIG. 3 is a sectional view showing a sectional structure of a first area2 of the optical disk 1 shown in FIG. 1;

FIG. 4 is an enlarged view showing a second area 3 of the optical disk 1shown in FIG. 1 and a plan view showing a planar structure of a long pit107;

FIG. 5 is a sectional view and a block diagram showing a method offorming a non-reflecting portion 106 of the optical disk 1 shown in FIG.1;

FIGS. 6A, 6B and 6C show signal waveforms of reproduced signals whichare obtained during reproduction of information in an area of thenon-reflecting portion 106 of the optical disk 1 shown in FIG. 1, inwhich the signal waveforms are proportional to the intensity ofreflected light relative to a circumferential length, wherein FIG. 6A isa waveform chart of the signal waveform of the reproduced signal at alow degree of modulation, FIG. 6B is a waveform chart of the signalwaveform of the reproduced signal at a high degree of modulation, andFIG. 6C is a waveform chart of the signal waveform of the reproducedsignal at a high degree of modulation and in a defocus state;

FIG. 7 is a block diagram showing a configuration of a first areadetecting circuit 23 a for use in the first preferred embodiment of theinvention;

FIG. 8 is a plan view showing a planar structure of the long pit 107formed in the second area 3 of the optical disk 1 shown in FIG. 1;

FIGS. 9A and 9B show a sectional structure of the long pit 107 shown inFIG. 8, wherein FIG. 9A is a sectional view taken along the line A-A′ ofFIG. 8 located in the center of the long pit 107, and FIG. 9B is asectional view taken along the line B-B′ of FIG. 8 located in an endportion of the long pit 107;

FIG. 10 is a block diagram showing a configuration of a second areadetecting circuit 24 a for use in the first preferred embodiment of theinvention;

FIGS. 11A, 11B and 11C show a method of detecting the second area by thesecond area detecting circuit 24 a shown in FIG. 10, wherein FIG. 11A isa waveform chart of a signal waveform of a reproduced signal in an areaincluding the area of the long pit 107, FIG. 11B is a waveform chart ofa signal waveform of an output signal CV1 from a comparator 8 shown inFIG. 10, which uses a first threshold value voltage V1th, and FIG. 11Cis a waveform chart of a signal waveform of an output signal CV2 from acomparator 9 shown in FIG. 10, which uses a second threshold valuevoltage V2th;

FIG. 12 shows a table of waveform charts of signal waveforms ofreproduced signals which are obtained during reproduction of informationin the area of the non-reflecting portion 106 and the area of the longpit 107 on each optical disk, where FIG. 12(a) shows waveform charts ofthe signal waveforms of the reproduced signals which are obtained duringreproduction of information in the area of the non-reflecting portion106 and the area of the long pit 107 on the authorized optical disk 1according to the first preferred embodiment of the invention, FIG. 12(b)shows waveform charts of the signal waveforms of the reproduced signalswhich are obtained during reproduction of information in the area of thenon-reflecting portion 106 and the area of the long pit 107 on a firstpirated optical disk, and FIG. 12(c) shows waveform charts of the signalwaveforms of the reproduced signals which are obtained duringreproduction of information in the area of the non-reflecting portion106 and the area of the long pit 107 on a second pirated optical disk;

FIG. 13 is a plan view showing a planar structure of an optical disk 1 aaccording to a second preferred embodiment of the invention;

FIG. 14 is a block diagram showing a configuration of a first areadetecting circuit 23 for use in the second preferred embodiment of theinvention;

FIG. 15 is a block diagram showing a configuration of a second areadetecting circuit 24 for use in the second preferred embodiment of theinvention;

FIG. 16 is a block diagram showing a configuration of an optical diskreproducing apparatus for use in a third preferred embodiment of theinvention;

FIG. 17 shows a method of detecting the first area 2 for use in theoptical disk reproducing apparatus shown in FIG. 16 and is an enlargedplan view showing the correlation from each track on the optical disk 1in a circumferential direction to the first area 2;

FIG. 18 is a flow chart of a first portion of processing for detectingand judging the first area to be executed by a system controller 25shown in FIG. 16; and

FIG. 19 is a flow chart of a second portion of the processing fordetecting and judging the first area to be executed by the systemcontroller 25 shown in FIG. 16.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An optical disk, an optical disk reproducing method and an optical diskreproducing apparatus according to preferred embodiments of theinvention will be described below with reference to the accompanyingdrawings. Herein, optical disks include an optical disk and amagneto-optical disk such as a CD, a video CD, a CD-ROM, a CD-R, aCD-RW, an MD, a DVD, a DVD-ROM, a DVD-RAM and a DVD-RW.

First Preferred Embodiment

FIG. 1 is a plan view showing a planar structure of an optical disk 1according to a first preferred embodiment of the invention, FIG. 2 is asectional view showing a sectional structure of the optical disk 1 shownin FIG. 1, FIG. 3 is a sectional view showing a sectional structure of afirst area 2 of the optical disk 1 shown in FIG. 1, and FIG. 4 is anenlarged view showing a second area 3 of the optical disk 1 shown inFIG. 1 and a plan view showing a planar structure of a long pit 107.

FIG. 1 shows a planar structure of an information recording area of theoverall optical disk 1. The information recording area comprises alead-in area 111 for recording control information, a data recordingarea 112 that is a user data recording area for recording contentinformation composed of content control information and content data,and a lead-out area 113. The optical disk 1 has a rotation driving hole1 h in the center thereof. The lead-in area 111, the data recording area112 and the lead-out area 113 are located in an order from the inside ofthe optical disk 1 toward the outside thereof. In the data recordingarea 112, the first area 2, which will be described later in detail,extends so as to have a longitudinal direction in a radial direction ofthe optical disk 1, while the second area 3, which will be describedlater in detail, extends so as to have a longitudinal direction in acircumferential direction of the optical disk 1.

As shown in FIG. 2, the optical disk 1 is formed of a bonded structureof a transparent optical disk substrate 100 and an optical disksubstrate 102. A reflecting film 101 of a material such as aluminum orgold is formed, by using the sputtering method which has been alreadyknown to those skilled in the art, on one surface of the transparentoptical disk substrate 100 which is formed so that concavo-convex pitsare formed thereon based on a replica. Then, one surface of the opticaldisk substrate 102 made through another step is bonded onto the surfaceof the transparent optical disk substrate 100 on which the reflectingfilm 101 is formed, using an adhesive layer 103 made of anultraviolet-curing resin which is located between the two optical disksubstrates 100 and 102. After that, the bonded optical disk substrates100 and 102 are irradiated with ultraviolet rays, and this leads to theadhesive layer 103 being allowed to cure and thus the two optical disksubstrates 100 and 102 are firmly bonded to each other. As a result, theoptical disk 1 is made.

FIG. 3 shows a sectional structure of the first area 2 having anon-reflecting portion 106 formed by partly removing the reflecting film101 in the optical disk 1 shown in FIG. 1. A method of making thenon-reflecting portion 106 is disclosed in International Publication No.WO96/16401. With reference to the publication, the method of making thenon-reflecting portion 106 will be briefly described with reference toFIG. 5. The optical disk 1 completed by the method described above withreference to FIG. 2 is irradiated on the side of the transparent opticaldisk substrate 100 with pulse laser light emitted from a YAG pulse laser104 so that the pulse laser light is focused on the reflecting film 101by a condenser lens 105. Thus, the reflecting film 101 is partlyremoved. As a consequence, the non-reflecting portion 106 is formed inthe first area 2.

FIGS. 6A to 6C show signal waveforms of reproduced signals which areobtained during reproduction of information in an area of thenon-reflecting portion 106 of the optical disk 1 shown in FIG. 1. Inthis case, the signal waveforms are proportional to the intensity ofreflected light relative to a circumferential length. FIG. 6A is awaveform chart of the signal waveform of the reproduced signal at a lowdegree of modulation, FIG. 6B is a waveform chart of the signal waveformof the reproduced signal at a high degree of modulation, and FIG. 6C isa waveform chart of the signal waveform of the reproduced signal at ahigh degree of modulation and in a defocus state.

When information recorded in the first area 2 of the optical disk 1configured as described above with reference to FIG. 5 is reproduced byusing the optical disk reproducing apparatus, there are obtained thesignal waveforms of the reproduced signals including RF signals changingperiodically as shown in FIGS. 6A to 6C. At a low degree of modulation,a dark level of the periodic RF signal does not drop sufficiently. Inthis case, the dark level refers to the darkest level of an envelope ofthe RF signal, and is called an envelope bottom level. Therefore, asshown in FIG. 6A, the level of the reproduced signal in the area of thenon-reflecting portion 106 is compared with a threshold value, namely, afirst slice level that is lower than the envelope bottom level of the RFsignal by a predetermined amount of level shift, and then, the presenceof the non-reflecting portion 106 can be detected.

At a high degree of modulation, as shown in FIG. 6B, the envelope bottomlevel of the RF signal drops sufficiently. Thus, little or no differenceis made between the envelope bottom level of the RF signal and an outputlevel of the non-reflecting portion 106. Therefore, it is not easy todetect the non-reflecting portion 106. However, in this case, an opticalhead, i.e., an optical pickup of the optical disk reproducing apparatusis controlled so that a spot of the Laser light to be applied to theoptical disk 1 becomes in a defocus state. Thus, the envelope bottomlevel of the reproduced RF signal rises, and therefore, a significantdifference is made between the envelope bottom level of the RF signaland the level of the reproduced signal in the area of the non-reflectingportion 106. Consequently, the area of the non-reflecting portion 106can be easily detected. In actuality, when an attempt is made to makethe spot of the laser light on the optical disk 1 be in a defocus stateand to reproduce information recorded on the optical disk 1, areproduced clock signal, which is to be generated from the reproducedsignal by a PLL circuit in an analog processor, cannot be, in somecases, generated. Therefore, in some cases, the PLL circuit is heldimmediately before the spot of the laser light is made in a defocusstate, and the analog processor is controlled so as to hold andreproduce the reproduced clock signal in a state immediately before thedefocus state.

Furthermore, it may be a possible method to reproduce informationrecorded in the first area 2 by performing tracking of an area locatedbetween two adjacent tracks on the optical disk 1. In this case, in amanner similar to above, the envelope bottom level, i.e., the dark levelof the RE signal rises in any area other than the non-reflecting portion106, however, the reproduced clock signal cannot be generated due tocross-talk between the RE signals. Thus, a reproduced clock immediatelybefore tracking between the tracks is held and reproduced in a stateimmediately before tracking.

FIG. 7 is a block diagram showing a configuration of a first areadetecting circuit 23 a for use in the first preferred embodiment of theinvention. The first area detecting circuit 23 a comprises a data slicer4, an envelope bottom detecting circuit 5, a level shift circuit 6, anda comparator 7.

Referring to FIG. 7, the reproduced signal outputted from an analogprocessor 20 of FIG. 16 for applying analog signal processing to thereproduced signal from the optical disk 1 is inputted to the data slicer4, a first input terminal of the comparator 7 and the envelope bottomdetecting circuit 5. The data slicer 4 binarizes the reproduced signal,which is inputted from the optical disk 1 through the analog processor20, by using a predetermined threshold value. Thus, the data slicer 4converts the reproduced signal into digital data, i.e., a binarizedreproduced signal, and then, outputs the binarized reproduced signal. Onthe other hand, the envelope bottom detecting circuit 5 detects theenvelope bottom level that is the lowest level of the envelope of theinput reproduced signal, and then, outputs a low envelope signal havingthe detected envelope bottom level to the level shift circuit 6.Subsequently, the level shift circuit 6 shifts downward the envelopebottom level of the input low envelope signal by a predetermined amountof level shift (See FIGS. 6A and 6C), and then, outputs a thresholdvalue signal having the above-mentioned level-shifted first slice levelto a second input terminal of the comparator 7. Furthermore, thecomparator 7 compares the reproduced signal inputted to the first inputterminal with the threshold value signal having the first slice levelinputted to the second input terminal. When the level of the reproducedsignal is lower than the first slice level, i.e., in the area of thenon-reflecting portion 106, the comparator 7 outputs a low-level signalas a non-reflecting portion detecting signal. In the above-mentionedmanner, the area of the non-reflecting portion 106 in the first area 2having the reflecting film partly removed can be easily detected.

Next, description will be made with regard to the second area 3 having aconcavo-convex long pit 107 having a length longer than a maximum pitlength determined by a predetermined modulation method, i.e., having alength which is different from concavo-convex pits satisfying theabove-mentioned modulation method. As shown in the planar structures ofFIGS. 4 and 8, the long pit 107 having a length equivalent to about 100Tin the longitudinal direction parallel to the circumferential directionis formed in the second area 3, for example, provided that a pit lengthfor generally recording user data in the data recording area 112 is 3Tto 14T (where T denotes a length corresponding to one reproduced clocksignal). FIGS. 9A and 9B show a sectional structure of the long pit 107shown in FIG. 8. FIG. 9A is a sectional view taken along the line A-A′of FIG. 8 located in the center of the long pit 107. FIG. 9B is asectional view taken along the line B-B′ of FIG. 8 located in an endportion of the long pit 107.

As shown in FIGS. 9A and 9B, the long pit 107 has a sectional structurein which the curvature of each edge of a cross section of the long pit107 is larger at the position closer to the circumferential, i.e.,longitudinal center (referring to a portion located at the midpointposition between both end portions in the longitudinal direction). Thecross section in the center of the long pit 107 has a sectional shapeshown in FIG. 9A. The cross sections in both the end portions of thelong pit 107 have a sectional shape shown in FIG. 9B. The long pit 107having the above-mentioned sectional shape can be easily formed byappropriately setting conditions for forming the transparent opticaldisk substrate 100 of the optical disk 1, as well known.

FIG. 11A shows a signal waveform of a reproduced signal which isobtained when information recorded in the second area 3 is reproduced inthe circumferential direction. The horizontal axis shown in FIGS. 11A,11B and 11C represents the elapsed time corresponding to thecircumferential length when information recorded in the second area 3 isreproduced in the circumferential direction by moving the spot of thelaser light to be applied to the optical disk 1 at a constant speed.

As shown in FIG. 11A, as the spot of the laser light to be applied tothe optical disk 1 is moved from one end of the long pit 107 to thelongitudinal center of the long pit 107 in the circumferentialdirection, the level of the reproduced signal rises toward a brightlevel with a gradual gradient, and then, the level of the reproducedsignal reaches the brightest level in the area of the long pit 107 inthe longitudinal center of the long pit 107. Furthermore, as the spot ofthe laser light to be applied to the optical disk 1 is moved from thecenter of the long pit 107 to the other end of the long pit 107 in thecircumferential direction, the level of the reproduced signal dropstoward the dark level with a gradual gradient. The level of thereproduced signal changes in the area of the long pit 107 as mentionedabove for the following reason. As shown in FIG. 9A, the curvature ofthe edge of the long pit 107 in which interference occurs is larger inthe center of the long pit 107, thus a substantial pit depth D is notequal to a specified value, i.e., λ/4 (where λ denotes an averagewavelength of the laser light from an optical head 18), and, therefore,the level of the reproduced signal rises to the bright level.

Next, a method of identifying the second area 3 will be described withreference to FIGS. 10, 11A, 11B and 11C. FIG. 10 is a block diagramshowing a configuration of a second area detecting circuit 24 a for usein the first preferred embodiment of the invention. FIGS. 11A to 11Cshow a method of detecting the second area by the second area detectingcircuit 24 a shown in FIG. 10. FIG. 11A is a waveform chart of a signalwaveform of a reproduced signal in an area including the area of thelong pit 107. FIG. 11B is a waveform chart of a signal waveform of anoutput signal CV1 from a comparator 8 shown in FIG. 10, which uses afirst threshold value voltage V1th close to the bright level. FIG. 11Cis a waveform chart of a signal waveform of an output signal CV2 from acomparator 9 shown in FIG. 10, which uses a second threshold valuevoltage V2th close to the dark level.

Referring to FIG. 10, the second area detecting circuit 24 a comprisesthe data slicer 4, the two comparators 8 and 9, two threshold valuevoltage generators 8 a and 9 a, two counters 10 and 11, and a normallength pit discriminating circuit 12. In FIG. 10, the same components asthe components shown in FIG. 7 are indicated by the same referencenumerals.

Referring again to FIG. 10, the reproduced signal outputted from theanalog processor 20 of FIG. 16 for applying analog signal processing tothe reproduced signal from the optical disk 1 is inputted to the dataslicer 4 and the respective first input terminals of the two comparators8 and 9. The data slicer 4 binarizes the reproduced signal, which isinputted from the optical disk 1 through the analog processor 20, byusing a predetermined threshold value. Thus, the data slicer 4 convertsthe reproduced signal into digital data, i.e., a binarized reproducedsignal, and then, outputs the binarized reproduced signal. On the otherhand, the first threshold value voltage V1th from the threshold valuevoltage generator 8 a is inputted to a second input terminal of thecomparator 8. The comparator 8 compares the reproduced signal inputtedto the first input terminal to the first threshold value voltage V1thclose to the bright level, and then, outputs a comparison result signalto the counter 10. When the level of the reproduced signal is equal toor higher than the first threshold value voltage V1th, the comparator 8outputs a high-level comparison result signal. In the other cases, thecomparator 8 outputs a low-level comparison result signal. Moreover, thesecond threshold value voltage V2th from the threshold value voltagegenerator 9 a is inputted to a second input terminal of the comparator9. The comparator 9 compares the reproduced signal inputted to the firstinput terminal with the second threshold value voltage V2th close to thedark level, and then, outputs a comparison result signal to the counter11. When the level of the reproduced signal is equal to or higher thanthe second threshold value voltage V2th, the comparator 9 outputs ahigh-level comparison result signal. In the other cases, the comparator9 outputs a low-level comparison result signal.

Each of the counters 10 and 11 counts channel bit clock signals pckwhich are reproduced from the reproduced signals by the analog processor20, during a valid time interval during which the input comparisonresult signal is at high level. Then, each of the counters 10 and 11outputs time data of a count result (corresponding to the time intervalT1 shown in FIG. 11B and the time interval T2 shown in FIG. 11C duringwhich the comparison result signal is at high level) to the normallength pit discriminating circuit 12. Subsequently, when the timeinterval T2 shown in FIG. 11C is equal to or longer than a predeterminedfirst threshold time and the time interval between the start of the timeinterval T2 (the leading edge of a pulse of the high-level comparisonresult signal in the time interval T2 in the area of the long pit 107)and the start of the time interval T1 (the leading edge of a pulse ofthe high-level comparison result signal in the time interval T1 in thearea of the long pit 107) is equal to or longer than a predeterminedsecond threshold time, the normal length pit discriminating circuit 12judges that the presence of the long pit 107, i.e., the presence of thesecond area 3 is detected, and then, the circuit 12 outputs a long pitdetecting signal.

In the case of a typical normal pit, in a form of which data of a signalmodulated according to using a predetermined modulation method isrecorded on the optical disk 1, the reproduced level of the normal pitabruptly or suddenly changes from the dark level to the bright level,and the time interval for the change is substantially fixed. However,the reproduced level of the above-mentioned long pit 107 graduallychanges from the dark level to the bright level with a more gradualgradient than the gradient of change in the typical normal pit.Therefore, the long pit 107 or the second area 3 can be easily detectedby using the above-described method, i.e., by using the second areadetecting circuit 24 a shown in FIG. 10.

Description will be made with regard to the case in which a pirate makesa so-called RF copy of the optical disk 1 as configured as describedabove. “RF copying” described herein refers to making a copy of theoptical disk is made by using a stamper made by the use of an RF signalthat is a reproduced signal from the optical disk 1.

Description will be made with reference to FIG. 12 with regard to thecase in which the optical disk 1 is made as mentioned above. FIG. 12shows a table of waveform charts of signal waveforms of reproducedsignals which are obtained during reproduction of information in thearea of the non-reflecting portion 106 and the area of the long pit 107on each optical disk. FIG. 12(a) shows waveform charts of the signalwaveforms of the reproduced signals which are obtained duringreproduction of information in the area of the non-reflecting portion106 and the area of the long pit 107 on the authorized optical disk 1according to the first preferred embodiment of the invention. FIG. 12(b)shows waveform charts of the signal waveforms of the reproduced signalswhich are obtained during reproduction of information in the area of thenon-reflecting portion 106 and the area of the long pit 107 on a firstpirated optical disk made by RF copying. FIG. 12(c) shows waveformcharts of the signal waveforms of the reproduced signals which areobtained during reproduction of information in the area of thenon-reflecting portion 106 and the area of the long pit 107 on a secondpirated optical disk made under changed conditions from forming thefirst pirated optical disk.

In general, the non-reflecting portion 106 of the pirated optical disk,which is made by making a RF copy of the reproduced signal of thenon-reflecting portion 106 as it is, is recorded as the long pit. Thelong pit 107 of the authorized optical disk is judged as the presence orabsence of the pit, and thus the long pit 107 of the pirated opticaldisk is recorded as if the length of the long pit 107 were reduced.

Therefore, as shown in FIG. 12, when information recorded on the piratedoptical disk is reproduced, the RF signal contains a long-time darklevel signal in an area corresponding to the first area 2 of theauthorized optical disk, and thus, it seems as if the long pit 107 wereformed in the above-mentioned area. However, the signal waveform of thereproduced signal that settles at the dark level and is continuous (Seea column of the area of the non-reflecting portion 106 shown in FIG.12(b)), or the signal waveform of the reproduced signal similar to thereproduced signal of the second area 3 of the authorized optical disk(See a column of the area of the non-reflecting portion 106 shown inFIG. 12(c)) is obtained in accordance with the forming conditions.

Information recorded in a portion corresponding to the second area 3 ofthe authorized optical disk is reproduced as a long bright levelsandwiched between short dark levels. When a pirated, unauthorizedoptical disk is copied by using the stamper made by the use of the RFsignal, a pit shorter than the normal long pit 107 is recorded.Moreover, the reproduced level of the shorter pit changes from the darklevel to the bright level more abruptly or suddenly than the long pit107 of the authorized optical disk (See a column of the area of the longpit 107 shown in FIG. 12(b) and FIG. 12(c)). As described above, it isjudged whether or not the optical disk is the authorized optical disk 1in accordance with a combination of the reproduced signal of thenon-reflecting portion 106 and the reproduced signal of the long pit107. Thus, it can be judged whether or not information recorded on theoptical disk 1 is reproduced.

As described above, according to the preferred embodiment, the opticaldisk, which is used for recording data of a signal modulated accordingto a predetermined modulation method in a form of concavo-convex pits,comprises the first area 2 having the reflecting film partly removed,and the second area 3 for recording pits which are different from pitssatisfying the requirements of the predetermined modulation method.Thus, the pirated optical disk is easily identified, and it can bejudged whether or not information recorded on the optical disk isreproduced. Therefore, the optical disk 1 capable of protecting theright of a copyright owner can be provided.

Second Preferred Embodiment

FIG. 13 is a plan view showing a planar structure of an optical disk 1 aaccording to a second preferred embodiment of the invention. The opticaldisk 1 a according to the second preferred embodiment is characterizedby that the optical disk 1 according to the first preferred embodimenthas a recording area called a BCA (Burst Cutting Area) 13 in whichlocation information of the first area is stored in a first arealocation information recording area 13 a and location information of thesecond area is stored in a second area location information recordingarea 13 b. The other structure of the optical disk la is the same asthat of the optical disk 1 according to the first preferred embodiment.When information recorded on the optical disk 1 a according to thesecond preferred embodiment is reproduced, whether or not the opticaldisk is the authorized optical disk la is more easily judged inaccordance with the location information recorded in the first arealocation information recording area 13 a and the second area locationinformation recording area 13 b in the BCA 13.

FIG. 14 is a block diagram showing a configuration of a first areadetecting circuit 23 for use in the second preferred embodiment of theinvention. In FIG. 14, the same components as the components of thefirst area detecting circuit 23 a shown in FIG. 7 are indicated by thesame reference numerals, and the detailed description thereof isomitted. In the present preferred embodiment, an address of thenon-reflecting portion 106 and an address of the long pit 107 arewritten in the BCA 13, and each of the addresses contains locationinformation composed of an ID number and the number of clocks.

Referring to FIG. 14, the first area detecting circuit 23 comprises awindow generating circuit 14, a counter 15, a latch 16, a BCAreproducing circuit 31 and an AND gate 32, in addition to the dataslicer 4, the envelope bottom detecting circuit 5, the level shiftcircuit 6 and the comparator 7.

The BCA reproducing circuit 31 reproduces information data recorded inthe BCA 13 of the optical disk 1 a, in particular, reproduces theaddress of the location information composed of the ID number and thenumber of clocks, and outputs the reproduced information data to thewindow generating circuit 14. Then, the window generating circuit 14generates a window signal for detecting the non-reflecting portion 106in accordance with the location information that is recorded in the BCA13 and reproduced from the BCA 13 by the BCA reproducing circuit 31, andthe circuit 14 outputs the window signal to a second input terminal ofthe AND gate 32. In other words, the window generating circuit 14compares the address contained in the reproduced signal with the addressof the location information in accordance with the reproduced signaloutputted from the analog processor 20 and the location information fromthe BCA reproducing circuit 31. When these addresses coincide with eachother, the window generating circuit 14 outputs a high-level windowsignal, and thus, enables a window. When these addresses does notcoincide with each other, the window generating circuit 14 outputs alow-level window signal, and thus, disables the window. After the countof the counter 15 is reset to zero in accordance with a reset signalfrom the analog processor 20, the counter 15 counts the channel bitclock signals pck, i.e., the reproduced clocks that are generated fromthe reproduced signals by the analog processor 20, and the counter 15outputs count data to the latch 16. The count data indicatescircumferential location information since the instant when the count isreset in accordance with the reset signal.

The non-reflecting portion detecting signal from the comparator 7 isinputted to a first input terminal of the AND gate 32. The AND gate 32outputs a high-level signal to the latch 16 only when both of two inputsignals are at high level. Therefore, the AND gate 32 outputs thehigh-level signal to the latch 16, when the non-reflecting portion 106is detected by the comparator 7 and the location information from theBCA 13 coincides with the location information of the reproduced signal.In response to the high-level signal, the latch 16 latches the countdata outputted from the counter 15 by the use of the non-reflectingportion detecting signal obtained during the valid time interval of thewindow generated by the window generating circuit 14, and then, thelatch 16 outputs correct detected location information.

FIG. 15 is a block diagram showing a configuration of a second areadetecting circuit 24 for use in the second preferred embodiment of theinvention. In FIG. 15, the same components as the components of thesecond area detecting circuit 24 a shown in FIGS. 14 and 10 areindicated by the same reference numerals.

The second area detecting circuit 24 according to the second preferredembodiment is characterized by the second area detecting circuit 24further comprising the BCA reproducing circuit 31 and the windowgenerating circuit 14, in addition to the data slicer 4, the twocomparators 8 and 9, the two threshold value voltage generators 8 a and9 a, the two counters 10 and 11, and the normal length pitdiscriminating circuit 12.

Referring to FIG. 15, in a manner similar to that of the BCA reproducingcircuit 31 and the window generating circuit 14 shown in FIG. 14, thewindow generating circuit 14 generates a window signal for detecting thelong pit 107 in accordance with the location information reproduced fromthe BCA 13 by the BCA reproducing circuit 31, and the circuit 14 outputsthe window signal to each of the counters 10 and 11. Only when ahigh-level window signal is inputted to each of the counters 10 and 11,the window generating circuit 14 opens the window, and causes thecounters 10 and 11 to operate only during the time interval of thewindow, and then, the normal length pit discriminating circuit 12 judgesthe presence or absence of the long pit 107.

Furthermore, a method of identifying the authorized optical disk 1 a byusing the first area detecting circuit 23 shown in FIG. 14, and thesecond area detecting circuit 24 shown in FIG. 15 will be described.

First of all, before reproducing the content information recorded on theoptical disk 1 a, the location information recorded in the BCA 13 isread out by using the BCA reproducing circuit 31. Then, the optical head18 shown in FIG. 16 is allowed to perform a seek in accordance with thelocation information, thereby reproducing information recorded in thefirst area 2. A method of detecting the non-reflecting portion 106 fromthe reproduced signal is the same as the method of the first preferredembodiment, and thus, the description thereof is omitted. The intensityof copyright protection further improves because of the addition ofjudgment about the presence or absence of the long pit 107 in thelocation recorded in the location information. Furthermore, the locationinformation recorded in the BCA 13 is read out by using the BCAreproducing circuit 31. Then, the optical head 18 shown in FIG. 16 isallowed to perform seeks in accordance with the location information,thereby reproducing information recorded in the second area 3. Then, thelegality of the long pit 107 is judged in accordance with the reproducedsignal. Whether or not the optical disk 1 a is authorized is judged inaccordance with detected signals from the reproduced signals of thefirst area 2 and the second area 3. Thus, there can be judged whether ornot information recorded on the optical disk 1 a is reproduced. Thus,the so-called RF copy can be prevented, and therefore, a copyright canbe more solidly or certainly protected.

In the present preferred embodiment, the location information recordedin the area 13 a for recording the location information of the firstarea 2 and the area 13 b for recording the location information of thesecond area 3 contains the address, for example. Specifically, as shownin FIGS. 14 and 15, the location information can be specified by theaddress of the ID number or the like, and the number of clocks of thechannel bit clock signals pck from a sector header to a detected sector.The location information recorded in the area 13 a for recording thelocation information of the first area 2 and the area 13 b for recordingthe location information of the second area 3 is not limited to this,and may be any other type of location information capable of specifyingthe respective locations of the non-reflecting portion 106 and the longpit 107.

As described above, according to the present preferred embodiment, theoptical disk 1 a, which is provided for recording data of a signalmodulated according to a predetermined modulation method in a form ofconcavo-convex pits, comprises the first area 2 having thenon-reflecting portion 106 formed by partly removing the reflectingfilm, and the second area 3 for recording the long pit 107 which isdifferent from pits satisfying the requirements of the predeterminedmodulation method. Moreover, for example, the BCA 13 includes the firstarea location information recording area 13 a for recording the locationinformation of the first area 2 on the optical disk 1 a, and the secondarea location information recording area 13 b for recording the locationinformation of the second area 3 on the optical disk 1 a. Thenon-reflecting portion 106 formed in the first area 2 and the long pit107 formed in the second area 3 are identified by specifying therespective positions of the areas 2 and 3 in accordance with thelocation information recorded in the first area location informationrecording area 13 a and the second area location information recordingarea 13 b. Thus, the authorized optical disk 1 a is more easilyidentified at high speed. Therefore, there can be judged whether or notinformation recorded on the optical disk 1 a is reproduced.

Third Preferred Embodiment

FIG. 16 is a block diagram showing a configuration of an optical diskreproducing apparatus for use in a third preferred embodiment of theinvention. The optical disk reproducing apparatus according to the thirdpreferred embodiment comprises the optical head 18, a head amplifier 19,the analog processor 20, an optical disk controller 21, a servo controlcircuit 22, the first area detecting circuit 23, the second areadetecting circuit 24, a system controller 25, and a processing memory40. In FIG. 16, the optical disk 1 may be replaced with the optical disk1 a according to the second preferred embodiment.

Referring to FIG. 16, a spindle motor 17 rotates the optical disk 1 at apredetermined number of revolutions. The optical head 18 includes alaser diode and a photo-detector, and comprises the so-called opticalpickup. A signal reproduced by the optical head 18 is inputted to theanalog processor 20 through the head amplifier 19 for amplifying thesignal. The analog processor 20 has facilities for AGC, equalizing, dataslice, PLL and so on. The analog processor 20 applies predeterminedanalog processing to the input analog reproduced signal, and outputs theprocessed analog signal to the optical disk controller 21, the firstarea detecting circuit 23 and the second area detecting circuit 24.Furthermore, the optical disk controller 21 demodulates the reproducedsignal data, and applies error correction or the like to the data.Furthermore, the servo control circuit 22 controls the spindle motor 17and the optical head 18, thereby servo-controlling focusing, trackingand the like.

The first area detecting circuit 23 comprises the circuit according tothe second preferred embodiment shown in FIG. 14, for example. Inaccordance with the reproduced signal outputted from the analogprocessor 20, the first area detecting circuit 23 detects the first area2 having the non-reflecting portion 106 formed by partly removing thereflecting film, and then, the circuit 23 outputs the detected locationinformation. The first area detecting circuit 23 may be replaced withthe first area detecting circuit 23 a according to the first preferredembodiment shown in FIG. 7. The second area detecting circuit 24comprises the circuit according to the second preferred embodiment shownin FIG. 15, for example. In accordance with the reproduced signaloutputted from the analog processor 20, the second area detectingcircuit 24 detects the second area 3 having the long pit 107 which isdifferent from pits satisfying requirements of a predeterminedmodulation method, and has a length not satisfying any requirement ofthe above-mentioned modulation method. Then, the circuit 24 outputs thelong pit detecting signal. The second area detecting circuit 24 may bereplaced with the second area detecting circuit 24 a according to thefirst preferred embodiment shown in FIG. 10. The system controller 25 isa controller for controlling operation of the whole optical diskreproducing apparatus shown in FIG. 16 by using the processing memory40.

An operation of the optical disk reproducing apparatus configured asdescribed above will be described with reference to FIG. 17.

FIG. 17 shows a method of detecting the first area 2 for use in theoptical disk reproducing apparatus shown in FIG. 16, and is an enlargedplan view showing a correlation between each track on the optical disk 1in the circumferential direction and the first area 2. In the presentpreferred embodiment, it is assumed that the location information of thefirst area 2 having the non-reflecting portion 106 is previously storedin the BCA 13, and that the contents of the location information arecomposed of a sector address of a sector containing the first area 2 andthe number of data (or the number of clocks) from the sector header tothe above-mentioned detected sector. A method of detecting the secondarea 3 having the long pit 107 is the same as the method of using thesecond area detecting circuit 24 according to the second preferredembodiment, and thus, the description thereof is omitted.

FIGS. 18 and 19 are flow charts of processing for detecting and judgingthe first area to be executed by the system controller 25 shown in FIG.16.

In step S1 of FIG. 18, first of all, the servo control circuit 22 andthe optical disk controller 21 are controlled so as to read out datafrom the BCA 13, and the location information of the first area 2 readout from the BCA 13 is read out and stored in the processing memory 40.Subsequently, in step S2, as shown in FIG. 17, a command for controllingthe servo control circuit 22 to seek the n-th track containing a sectoraddress ID(n) including the first area 2 is issued in accordance withthe location information stored in the processing memory 40, then thetrack containing the sector address ID(n) is sought, and informationrecorded on the sought track is reproduced. Furthermore, in step S3, itis judged whether or not the first area 2 is detected duringreproducing. Until YES is given, the processing of step S3 is repeated.When YES is given, in step S4, the first area detecting circuit 23detects detected location information containing the address of thedetected sector and the number of data from the sector header to thedetected sector, and reads in the detected location information. Then,in step S5, the detected location information detected by the first areadetecting circuit 23 is compared with the location information of thefirst area 2 previously stored in the processing memory 40. In step S6,it is judged whether or not the detected location information coincideswith the location information of the first area 2. When the detectedlocation information does not coincide with the location information ofthe first area 2 in step S6 (NO in step S6), the processing returns tostep S2, and the above-mentioned processing is repeated in order toagain detect the first area 2. On the other hand, when the detectedlocation information coincides with the location information of thefirst area 2 in step S6 (YES in step S6), in step S7, as shown in FIG.17, the servo control circuit 22 is controlled so as to trace the sametrack (the n-th track). In step S8, it is judged whether or not the samesector address ID(n) is detected. Until the same sector address ID(n) isdetected, the processing of step S8 is repeated. When the same sectoraddress ID(n) is detected in step S8, the flow goes to step S9 of FIG.19.

In step S9 of FIG. 19, the servo control circuit 22 is controlled sothat the optical head 18 jumps to an adjacent next track. At this time,at least the PLL circuit included in the analog processor 20 is held soas to prevent the PLL circuit from tracking, since the number of clocksis counted by the first area detecting circuit 23. In the presentpreferred embodiment, as shown in FIG. 17, whether or not the first area2 is detected on the adjacent track, namely, the (n+1)-th track by thefirst area detecting circuit 23 is similarly checked or confirmed. Thenumber of data (or the number of clocks) from the sector address ID(n)on the n-th track to the first area 2 on the n-th track detected by thefirst area detecting circuit 23 is substantially equal to the number ofdata (or the number of clocks) from the sector address ID(n) on the n-thtrack to the first area 2 on the adjacent track (detected by the firstarea detecting circuit 23). Thus, the numbers of data detected by thefirst area detecting circuit 23 must substantially coincide with eachother. When both the detected numbers of data are substantially equal toeach other, the system controller 25 judges that the detected area isthe first area 2 formed by removing the reflecting film. Specificprocessing corresponds to the processing from step S10 to step S13.

Then, in step S10, the number of data (or the number of clocks) from thesector address ID(n) on the n-th track to the first area 2 on the n-thtrack is compared with the number of data (or the number of clocks) fromthe sector address ID(n) on the n-th track to the first area 2 on theadjacent (n+1)-th track. In step S11, it is judged whether or not thenumbers of data substantially coincide with each other. In this case,the number of data may be counted or the number of clocks may becounted, because data corresponding to clock signals are present. Acriterion of judgment as to whether or not the numbers of datasubstantially coincide with each other is determined in the followingmanner. Judgment is made that two types of the numbers of datasubstantially coincide with each other, as long as a difference betweenthe numbers of data is within a few clocks such as 2 or 3 clocks (or afew pieces of data). When the answer is YES in step S11, in step S12,judgment is made that the detected area is the first area 2 formed byremoving the reflecting film, and the processing for detecting andjudging the first area is ended. On the other hand, when the answer isNO in step S11, in step S13, judgment is made that the detected area isnot the first area 2, and the processing for detecting and judging thefirst area is ended.

The processing for detecting and judging the first area described withreference to FIGS. 18 and 19 utilizes the fact that a size of the firstarea 2 in the radial direction cannot be about the same as the size of atrack pitch and, thus, the first area 2 extends over at least aplurality of tracks. In the present preferred embodiment, the systemcontroller 25 makes the judgment by using the result of detection of thesecond area using the second area detecting circuit 24 as mentioned inthe description of the second preferred embodiment, in addition to theprocessing for detecting and judging the first area. Thus, the systemcontroller 25 judges whether or not information recorded on the opticaldisk is reproduced. Therefore, the system controller 25 can moreaccurately judge whether or not the optical disk is the authorizedoptical disk.

As described above, the first area 2 formed by removing the reflectingfilm is detected based on a sector, and is further detected based on thenumber of data or the number of clocks from a predetermined sector on anadjacent track thereof. Thus, an authorized optical disk can be easilydiscriminated from, for example, a pirated copy called an RF copy madeby synchronously driving a reproducing system and a recording system,because both of the systems require very strict rotation accuracy orprecision.

Modified Preferred Embodiments

In the above-described preferred embodiments, the optical diskreproducing apparatus comprises the first area detecting circuit 23 or23 a and the second area detecting circuit 24 or 24 a. However, theinvention is not limited to this. The optical disk reproducing apparatusmay comprise either the first area detecting circuit or the second areadetecting circuit.

Advantages Effects of Preferred Embodiments

As described in detail above, according to the invention, an opticaldisk, which is provided for recording data of a signal modulatedaccording to a predetermined modulation method in a form ofconcavo-convex pits, comprises a first area having a reflecting filmpartly removed, and a second area for recording pits which are differentfrom pits satisfying the requirements of the predetermined modulationmethod. Thus, a pirated optical disk is easily identified, and it can bejudged whether or not information recorded on the optical disk isreproduced. Therefore, the right of a copyright owner can be certainlyprotected.

Moreover, the optical disk further comprises a first area locationinformation recording area recording location information of the firstarea, and a second area location information recording area recordinglocation information of the second area. Thus, the first area and thesecond area can be specified in accordance with the location informationof the first area and the location information of the second area.Therefore, the first area and the second area can be more easilyidentified at high speed. Accordingly, the optical disk of the inventionhas a great practical merit.

Furthermore, the first area is again detected on an adjacent track todetect the first area formed by removing the reflecting film, and then,it is judged whether or not information recorded on the optical disk isreproduced. Therefore, the right of a copyright owner can be certainlyprotected, and measures to more solidly protect against a pirated copycan be provided.

Although the present invention has been fully described in connectionwith the preferred embodiments thereof with reference to theaccompanying drawings, it is to be noted that various changes andmodifications are apparent to those skilled in the art. Such changes andmodifications are to be understood as included within the scope of thepresent invention as defined by the appended claims unless they departtherefrom.

1. An apparatus for reproducing information recorded on an optical diskwhich is provided for recording data of a signal modulated according toa predetermined modulation method in a form of concavo-convex pits, saidoptical disk comprising a first area having a reflecting film partlyremoved, and a second area for recording pits which are different frompits satisfying requirements of said predetermined modulation method,said apparatus comprising: a first area detecting circuit for detectingsaid first area in accordance with a reproduced signal from said opticaldisk upon reproducing information recorded in said first area, andoutputting a first detecting signal; a second area detecting circuit fordetecting said second area in accordance with a reproduced signal fromsaid optical disk upon reproducing information recorded in said secondarea, and outputting a second detecting signal; and judging means forjudging whether or not the information recorded on said optical diskshould be reproduced, in accordance with said first and second detectingsignals, wherein said second area detecting circuit comprises: a firstcomparator for comparing the reproduced signal from said optical diskupon reproducing information recorded in said second area, with apredetermined first threshold value, and outputting a first comparisonresult signal; a second comparator for comparing the reproduced signalfrom said optical disk upon reproducing information recorded in saidsecond area, with a predetermined second threshold value, and outputtinga second comparison result signal; and an arithmetic logic circuit forperforming a logic operation between said first comparison result signaland said second comparison result signal, and outputting a logicoperation result signal, wherein said first area detecting circuitjudges whether or not said first area is detected in accordance withwhether or not a first number of data from a predetermined sectoraddress to said detected first area, which is counted based on thereproduced signal from said optical disk upon reproducing informationrecorded on a track including said first area, substantially coincideswith a second number of data from said predetermined sector address tosaid detected first area, which is counted based on a reproduced signalfrom said optical disk upon reproducing information recorded on afurther track including said first area and adjacent to said track. 2.An apparatus for reproducing information recorded on an optical diskwhich is provided for recording data of a signal modulated according toa predetermined modulation method in a form of concavo-convex pits, saidoptical disk comprising a first area having a reflecting film partlyremoved, a second area for recording pits which are different from pitssatisfying requirements of said predetermined modulation method, a firstarea location information recording area for recording locationinformation of said first area on said optical disk, and a second arealocation information recording area for recording location informationof said second area on said optical disk, said apparatus comprising: afirst detecting window generating circuit for generating a firstdetecting window signal in accordance with said location information ofsaid first area on said optical disk recorded in said first arealocation information recording area; a second detecting windowgenerating circuit for generating a second detecting window signal inaccordance with said location information of said second area on saidoptical disk recorded in said second area location information recordingarea; a first area detecting circuit for detecting said first area inaccordance with a reproduced signal from said optical disk uponreproducing information recorded in said first area, and outputting afirst detecting signal; a second area detecting circuit for detectingsaid second area in accordance with a reproduced signal from saidoptical disk upon reproducing information recorded in said second area,and outputting a second detecting signal; and judging means for judgingwhether or not the information recorded on said optical disk should bereproduced, in accordance with said first detecting signal in a validtime interval of said first detecting window signal, and said seconddetecting signal in a valid time interval of said second detectingwindow signal, wherein said second area detecting circuit comprises: afirst comparator for comparing the reproduced signal from said opticaldisk upon reproducing information recorded in said second area, with apredetermined first threshold value, and outputting a first comparisonresult signal; a second comparator for comparing the reproduced signalfrom said optical disk upon reproducing information recorded in saidsecond area, with a predetermined second threshold value, and outputtinga second comparison result signal; and an arithmetic logic circuit forperforming a logic operation between said first comparison result signaland said second comparison result signal, and outputting a logicoperation result signal, wherein said first area detecting circuitjudges whether or not said first area is detected in accordance withwhether or not a first number of data from a predetermined sectoraddress to said detected first area, which is counted based on thereproduced signal from said optical disk upon reproducing informationrecorded on a track including said first area, substantially coincideswith a second number of data from said predetermined sector address tosaid detected first area, which is counted based on a reproduced signalfrom said optical disk upon reproducing information recorded on afurther track including said first area and adjacent to said track.